1. Field of the Invention
The present invention relates to a direct-illumination backlight apparatus using LEDs as a light source, more particularly, which is designed to introduce a partial light from an LED light source at such an angle that the partial light is trapped inside the transparent plate, and then scatter the trapped light beam at a position directly above the LED light source so that the scattered light beam escapes out of the transparent plate toward an LCD panel, thereby removing any dark area above the LED light source in the transparent plate and thus reducing its thickness.
2. Description of the Related Art
Liquid crystal display (LCD) backlight apparatuses using LEDs illuminate an LCD panel via direct-illumination or side-emitting illumination. In the side-emitting illumination, light from a light source is emitted in lateral directions and then re-directed upward via a reflective plate or a scattering pattern to illuminate the LCD panel. On the contrary, in the direct-illumination, light sources are installed under the LCD panel so that light emitted laterally from the light sources are projected upward onto the LCD panel.
FIG. 1 is a schematic cross-sectional view of a conventional side-emitting backlight apparatus. As shown in FIG. 1, the side-emitting backlight apparatus includes a reflective plate 12 having scattering patterns 14 formed thereon, a light guide plate 16 disposed on the reflective plate 12 and bar type LED light sources 18 and 20 disposed at both sides of the light guide plate 16.
The LED light sources 18 and 20 emit light L laterally into the light guide plate 16. Then, light L propagates through the light guide plate 16, and when colliding against the scattering patterns 14, is scattered upward thereby backlighting an LCD panel 22 above the light guide plate 16.
The side-emitting backlight apparatus 10 as above advantageously has a thin and simple structure. Another advantage of this backlight apparatus is that the intensity of light directed upward can be uniformly adjusted through the design of the scattering patterns 14 formed in the top face of the reflective plate 12 or the underside of the light guide plate 16. However, this structure is not applicable to a large-sized LCD since light from the LED light sources 18 and 20 can be sent to a limited distance only.
FIG. 2 is a schematic cross-sectional view of a conventional direct-illumination backlight apparatus. The direct-illumination backlight apparatus 30 includes a flat reflective sheet 32, a plurality of bar-shaped LED light sources 34 placed on the reflective sheet 32, reflective plates or light shades 36 placed on the LED light sources 34, respectively, a transparent plate 38 placed above the light shades 36 at a predetermined gap G1 and a diffuser plate 40 placed above the transparent plate 38 at a predetermined gap G2.
The LED light sources 34 emit lights L1 and L2 substantially in horizontal directions, and emitted light L1 is reflected from the reflective sheet 32 and passes through the transparent plate 38. Then, light L1 is diffused by the diffuser plate 40 to a desired uniformity to backlight an LCD panel placed above the diffuser plate 40. Another light L2 comes into contact with the underside of the transparent plate 38 so that a part L21 thereof enters by the transparent plate 38 and passes through the diffuser plate 40 above the transparent plate thereby backlighting the LCD panel. Meanwhile, another part L22 of the light L2 is reflected by the transparent plate 38 to the reflective sheet 32 and then reflected by the reflective sheet 32 to backlight the LCD panel 42 via the transparent plate 38 and the diffuser plate 40 like the light L1.
The backlight apparatus 30 of this structure has an advantage in that it can effectively backlight a large-sized LCD since the plurality of bar-shaped LED light sources 34 are placed under the LCD panel 42.
However, the backlight apparatus 30 of this structure disadvantageously increases thickness since the gap G1 is required between the LED light sources 34 and the transparent plate 38 and the gap G2 is also required between the transparent plate 38 and the diffuser plate 40.
Describing this in more detail, when generated from the LED light sources 34, light L is reflected upward through between the light shades 36, such that dark areas DA screened by the light shades 36 are formed. In order to remove the dark areas DA and the resultant bright lines, the gap G2 should be required to have at least a predetermined dimension to ensure a sufficient distance between the transparent plate 38 and the diffuser plate 40 so that light beams emitted from the transparent plate 38 can mix together before entering the diffuser plate 40.
As described above, since the gaps G1 and G2 are necessarily maintained at predetermined dimensions or more in order to impart uniformity to light directed from the reflective sheet 32 toward the LCD panel 42, the direct-illumination backlight apparatus 30 essentially suffers from thickness increase.